Small first step in expr_path. Call find_final_def just to detect

unresolved names. find_final_def is going to be extended to return the
final expr.

src/test/compile-fail/bad-expr-path.rs

@@ -0,0 +1,8 @@
+// error-pattern: unresolved name: a
+
+mod m1 {
+}
+
+fn main(vec[str] args) {
+  log m1.a;
+}